The present invention relates to a rubber composition for a bead and a pneumatic tire.
In recent years, demands for fuel efficiency are increasing and low heat generating tires are desired.
As a method to reduce heat generation, there are the method of reducing the amount of carbon black and the method of using carbon black having large particle size. However, in such methods, the hardness of the rubber decreases and as a result, there is the problem that stiffness of the tire decreases.
Particularly, stiffness of the bead is associated with steering performance and is extremely important. Therefore, rubber having extremely high hardness in comparison to other parts of a tire must be used for the bead. Consequently, the above methods are unsuitable for rubber of the bead and steering performance is impaired significantly.
On the other hand, to obtain high hardness, use of oil can be suppressed, but in such a case, viscosity of the compound rises and becomes load in the process. Also, high hardness can be obtained by adding thermosetting resin, but there is the problem that heat generation becomes large.
The method of using rubber containing carbon black and a thin plate-like natural mineral such as sericite in the rubber component for the tire tread in order to improve ozone resistance and performance on ice and for the sidewall of a tire in order to obtain low air permeability is already known (see JP-A-2004-27003). However, the method of using such rubber for the bead to improve balance in fuel efficiency and steering stability is not known.